EMI reduction technology in 85 kHz band 44 kW wireless power transfer system for rapid contactless charging of electric bus

A 44 kW wireless power transfer (WPT) system is being developed for rapid contactless charging in an electric bus in the 85 kHz band, the candidate frequency for a wireless charging system for light-duty vehicles that is currently undergoing standardization. For field operation of this WPT system using the 85 kHz band in Japan, permission for use as industrial facilities emitting radio waves is required under the Radio Act. A two-channel WPT system with currents of opposite phase in the two transmit pads of the channels is introduced to reduce radiated emissions to within the Radio Act limits of electromagnetic radiation disturbance by cancelling the emission from each channel. Then, the diagonal placement of the transmit pads for the two channels is proposed to avoid the interference between the two channels where the interference couplings become null. Finally, the measured emission of the 44 kW WPT system in a 10 m anechoic chamber is shown.